Lionheart, known as Climbs Quickly among his own kind, was a treecat and a scout of the Bright Water Clan. He was the first treecat actually seen stealing celery from the human colonists on Sphinx, as well as the first one to bond with a human.
In 1518 PD, Climbs Quickly was assigned by his clan to observe a group of human colonists on Sphinx as part of a planet-wide surveillance effort by the treecats; his group of colonists included eleven-year-old Stephanie Harrington and her family. Enticed by the smell of celery growing in the Harringtons' greenhouse, Climbs Quickly used the cover of a nighttime thunderstorm to steal two heads of celery, only to be observed (and photographed) by Stephanie Harrington as he made his exit. The brief encounter left both with some manner of mental connection; over the next few days, both found they could feel what direction the other was in relation to them, despite the great distance between each other.
It was through this connection that Climbs Quickly was able to follow Stephanie as she went out hang gliding on her own while searching for him using their link. He helped her after she crashed and defended the injured girl against an attacking hexapuma, being grievously wounded in the fight. Stephanie then defended him, mortally wounding the hexapuma with a vibro-knife before the bulk of the Bright Water Clan arrived to defend them both. During this phase of grave danger the two bonded, and Stephanie insisted he be brought back with her to have his injuries treated. (HHA1.1: ABF) He was treated successfully and recovered, though it was necessary to amputate his right foreleg just below the shoulder. (HHA2.2: WPD)
He came to live with the Harringtons at their homestead near the Copperwalls, and was given the name Lionheart, as suggested by Richard Harrington. Several months later, he and Stephanie met Tennessee Bolgeo, an alleged scientist willing to study treecats. Lionheart instantly knew that Bolgeo was trying to deceive them, but was unable to communicate this fact to his person or any human. Soon after, he and his sister and Stephanie caught Bolgeo trying to kidnap treecats and take them off-world. Lionheart was willing to lure an adolescent hexapuma into the criminal's path, but Stephanie wanted him alive and killed the creature. (SK1)
In late 1521 PD Lionheart became the first treecat to travel offworld to Manticore with Stephanie Harrington to attend Landing University. (SK3)